The long term objective of the research described in this application is to determine the significance of dopamine (DA)-sulfate, the predominant (about 98%) circulating form of DA, in mammals. The proposed investigations will determine if DA-sulfate is a precursor for any of the catecholamines (CA) in vivo in the dog. These studies have important implications for the field of basic CA synthesis and metabolic mechanisms. If DA-sulfate is converted to DA or norepinephrine (NE), then these studies will have broad implications for the treatment and causes of various diseases in which the CA are thought to be contributing factors, such as certain neurological, cardiovascular, and renal disorders. If DA-sulfate is found to cross the blood-CSF barrier, then it is conceivable that this compound could prove useful for treating certain CNS disorders, such as Parkinson's disease. Radiolabelled DA-sulfate isomers (3H-DA-3-0-sulfate and 3H-DA-4-0-sulfate) will be used to label the body pool of endogenous DA-sulfate in the dog. Sequential samples of blood plasma and urine will be collected and analyzed by HPLC with dual-electrode electrochemical detection coupled to a flow-through scintillation counter. Parameters describing distribution and elimination of DA-sulfate will then be determined. Results will be used to design experiments utilizing double-label steady-state infusion techniques. 14C-DA and 3H-DA-sulfate will be infused intravenously into anesthetized dogs until constant plasma specific activities of DA, DA sulfate, NE, and epinephrine are reached and maintained. Sequential samples of plasma, urine, and CSF will be collected and analyzed for each of the above compounds. Results will be interpreted to provide quantitative answers to each of the following questions: 1. Is DA-sulfate a direct and/or indirect (via DA) precursor of NE in vivo? 2. Is DA-sulfate a significant source of free DA? 3. Is DA-sulfate a normal metabolite of DA? 4. Does the kidney contribute DA or DA-sulfate to the urine? 5. Does DA-sulfate enter the CSF from the blood?